1. Field of the Invention
The invention relates to a vehicle control system and a vehicle control method.
2. Description of the Related Art
In recent years, vehicle control called “torque demand control” is performed under which a target acceleration as an acceleration requested by the driver is determined based on a vehicle speed of the vehicle, and an accelerating operation amount (accelerator pedal stroke, pedal effort, etc.) at the time when the driver operates an accelerator pedal, and the throttle opening, fuel injection amount, ignition timing, etc. of the engine are controlled based on the target acceleration thus determined, as described in, for example, Japanese Patent Application Publication No. 63-025342 (JP-A-63-025342). While the target acceleration is determined based on the vehicle speed and the accelerating operation amount under the known torque demand control, the determined target acceleration, which is based on the senses of expert evaluators, provides a poor ground for achieving high-quality acceleration performance or acceleration feeling that is favorable for any driver, and it is thus difficult to design the optimum target acceleration.
Some examples of the torque demand control utilize the Weber-Fechner's law, as described in, for example, Japanese Patent Application Publication No. 2008-254600 (JP-A-2008-254600), Japanese Patent Application Publication No. 2009-057874 (JP-A-2009-057874), Japanese Patent Application Publication No. 2009-057875 (JP-A-2009-057875) and Japanese Patent Application Publication No. 2009-083542 (JP-A-2009-083542). According to the Weber-Fechner's law, “the quantity of human perception is proportional to the logarithm of the physical quantity of stimulus applied thereto”. In the torque demand control utilizing the Weber-Fechner's law, a required value is determined based on the vehicle speed, the accelerating operation amount, and an exponential function utilizing the Weber-Fechner's law, and output control of the engine, etc. is performed based on the required value. In the known torque demand control as described above, the acceleration drops at a higher rate as the vehicle speed increases, or it takes much time to reach a steady-state condition with the same accelerating operation amount, resulting in an increase of the vehicle speed, whereby the driver may feel uncomfortable.
With the torque demand control utilizing the Weber-Fechner's law, too, it is difficult to design the optimum target acceleration in relation to the driver's accelerating operation amount, and the control is not sufficient to achieve an acceleration that meets or agrees with the sensibility of the driver, thus leaving room for improvement.